In an exhaust gas purification system for an internal combustion engine having a particulate filter (hereinafter referred to as a filter) arranged on an exhaust passage of the internal combustion engine for trapping particulate matter (hereinafter referred to as PM) in an exhaust gas, filter regeneration control for oxidizing PM deposited or accumulated in the filter for removal thereof is carried out by raising the temperature of the filter to a target temperature.
In addition, in Japanese patent application laid-open No. 2003-27990, there is disclosed a technique in which when the operating state of an internal combustion engine becomes a low-load, low-speed rotational operation during the execution of filter regeneration control, the amount of an EGR gas is increased, and at the same time, the amount of intake air is decreased and an amount of fuel corresponding to the amount of oxygen, which will become surplus or excessive after injection of main fuel, is injected as auxiliary fuel injection.
Further, Japanese patent application laid-open No. 2003-172124 discloses a technique in which the amount of auxiliary fuel to be injected is increased when the operating state of an internal combustion engine becomes idle during the execution of filter regeneration control more than in a normal or ordinary operating state thereof. Additionally, techniques related to filter regeneration control are also disclosed in Japanese patent application laid-open No. 2002-188493 and Japanese utility model application laid-open No. H03-104138, respectively.